1. Field of the Invention
The invention relates in general to a wheelchair, and in particular, to a human powered wheelchair utilizing both a forward and a rearward linear motion to convert linear movement to into rotative movement of the wheels, wherein the hub of the wheel is capable of controlled rotation in the event of inappropriate gearing selection, and where the user can comfortably utilize the wheelchair for an extended period of time.
2. Background Art
Wheelchairs have long been known in the art. Generally, it is most desirable to convert the maximum possible energy of the user to the movement of the wheelchair in the desired direction. Specifically, with the least amount of effort, the user should be able to control various parameters of the wheelchair movement to enable controlled travel for extended periods of time. While many wheelchair improvements have been attempted, most of these include deficiencies which render them little more effective than a conventional wheelchair. Further, many of these wheelchairs that have been created are limited by complex designs that are neither efficient nor easily used and/or maintained.
The manual wheelchairs can be divided into four general categories. The first category includes wheelchairs which are powered by hand to impart forces to an outer rim proximate the outer tire of the wheelchair. These chairs have certain benefits inasmuch as they are relatively easy to maneuver. For instance, the wheelchair can be rotated in place by rotating one wheel in a first direction and rotating the second wheel in a second direction. However, these wheelchairs do suffer from certain drawbacks. For instance, the user, after imparting energy from the hands to the wheel, must move the hand back to its original position so that the working stroke can be repeated. Thus, for half of the movement of the wheel the user's hands are not even touching the rim, much less transferring any energy to the wheel. Further, due to the position of the user relative to the wheel, it is difficult to impart energy efficiently to the wheel. In fact, only a portion of the user's strength is available for transfer to the wheel, and only through a small angle of rotation of the wheel. Moreover, the user's positioning is rather uncomfortable throughout the working stroke to the wrists, hands, arms, shoulders, and throughout the body. This may cause further injury in certain situations, especially after prolonged use.
The second type of wheelchair comprises the use of a highly positioned handle which is associated with eccentrically fastened crank that converts linear movement of the handle into rotative movement of the drive wheel. Such wheelchairs date to the early 1900's. One such example can be seen in U.S. Pat. No. 4,993,732. Such a wheelchair can exhibit positive results on flat terrain. However, these wheelchairs exhibit certain drawbacks with respect to maneuvering, as well as travel on inclined surfaces. Moreover, the repetitive powering by a user is quite tiring on the muscles.
Specifically, due to human physiology, these wheelchairs are less than ideal. In fact, while they may be well suited for a user that has full use of the lower body, to most users confined in a wheelchair, this is not the case. Where the user does not have control of the lower body extremities, these wheelchairs are difficult to operate, inasmuch as the user cannot use his or her lower body to counteract the undesirable forces that are created by the upper body. Moreover, the use of this type of wheelchair focuses on only a small group of the user's muscles.
The third group of wheelchairs comprises the "pedal principle" driven wheelchairs. Such a wheelchair can be seen in U.S. Pat. Nos. 4,758,013 and 4,471,972. Specifically, the user through a pedal-like system converts rotative movement of the hands, through a series of belts or chains to rotative movement of the front wheels. While these types of wheelchairs may accept gear changers, and, in turn, several gears, due to the relatively bulky construction, conventional wheelchair structures (two small wheels in the front and two large wheels in the rear) are difficult to operate. Further, even with specialized constructions, inherently poor and uncomfortable positioning of the user's hands results in difficulties with respect to maneuvering the wheelchair. Moreover, the inherent dead-spots in the cyclical movement of the "pedals" makes travel on inclined surfaces quite difficult.
The final group of wheelchairs comprises other solutions which serve to convert linear movement of the user's hands into rotative movement of the wheels of the wheelchair. While these other solutions serve to convert more of the user's energy to movement of the wheelchair than the prior three types, many of these chairs are incapable of safely transporting the users. Indeed, some of these chairs are so hazardous that more harm than good can be achieved. One such example is SI P 94 00 241, which has effectively sought to transfer energy, but has not fully addressed safety concerns and adaptability to users that are incapable of operating both of their hands. For example, this solution, as well as the others, do not adequate solve the following important design criteria:
facilitating the changing of gears during movement. Current devices rely on stopping or on chains with derailleurs. Thus, often when a gear change is most desirable, it is not possible; PA1 facilitating safety systems which prevent abrupt changes in the wheelchair operation should the user inadvertently engage the forward gears while traveling in reverse (or visa versa). In fact, changing from forward to reverse during forward movement would seize the gearing and catapult the user of a mechanism such as that described in SI P 94 00 241; and PA1 effective handles for facilitating proper transfer of energy and minimizing discomfort to the user to facilitate extensive and continuous use. The heretofore positioning and orientation of handles used in association with such wheelchairs have limited the forces that actually were transferred to the wheelchair, have resulted in hand, arm and shoulder injuries after repetitive and continuous use, and have adversely fatigued the user.